1. Field of the Invention
This invention relates to functional fluids and concentrates thickened with associative polyether thickeners. In addition to the associative polyether thickener, the fluids and concentrates also contain a cloud point raising additive which is a metal dialkyldithiophosphate, a polyether nonionic surfactant, preferably an alkanolamine, and other optional ingredients.
2. Description of the Prior Art
It is known to formulate functional fluids with associative polyether thickeners. See, for instance, U.S. Pat. Nos. 4,411,819 and 4,312,768. However, the fluids described in these patents have wear rates of approximately 20 milligrams per hour, and have cloud points of approximately 160.degree. F. Because of the high wear, these fluids are not satisfactory in pumps which operate under severe conditions such as vane pumps which may operate at high pressures (greater than 500 psi), or in systems which may have sump temperatures above 150.degree. F. or localized temperatures (such as where directional valves are placed) as high as 200.degree. F.